0001 =========
0002 dm-flakey
0003 =========
0004
0005 This target is the same as the linear target except that it exhibits
0006 unreliable behaviour periodically. It's been found useful in simulating
0007 failing devices for testing purposes.
0008
0009 Starting from the time the table is loaded, the device is available for
0010 <up interval> seconds, then exhibits unreliable behaviour for <down
0011 interval> seconds, and then this cycle repeats.
0012
0013 Also, consider using this in combination with the dm-delay target too,
0014 which can delay reads and writes and/or send them to different
0015 underlying devices.
0016
0017 Table parameters
0018 ----------------
0019
0020 ::
0021
0022 <dev path> <offset> <up interval> <down interval> \
0023 [<num_features> [<feature arguments>]]
0024
0025 Mandatory parameters:
0026
0027 <dev path>:
0028 Full pathname to the underlying block-device, or a
0029 "major:minor" device-number.
0030 <offset>:
0031 Starting sector within the device.
0032 <up interval>:
0033 Number of seconds device is available.
0034 <down interval>:
0035 Number of seconds device returns errors.
0036
0037 Optional feature parameters:
0038
0039 If no feature parameters are present, during the periods of
0040 unreliability, all I/O returns errors.
0041
0042 drop_writes:
0043 All write I/O is silently ignored.
0044 Read I/O is handled correctly.
0045
0046 error_writes:
0047 All write I/O is failed with an error signalled.
0048 Read I/O is handled correctly.
0049
0050 corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
0051 During <down interval>, replace <Nth_byte> of the data of
0052 each matching bio with <value>.
0053
0054 <Nth_byte>:
0055 The offset of the byte to replace.
0056 Counting starts at 1, to replace the first byte.
0057 <direction>:
0058 Either 'r' to corrupt reads or 'w' to corrupt writes.
0059 'w' is incompatible with drop_writes.
0060 <value>:
0061 The value (from 0-255) to write.
0062 <flags>:
0063 Perform the replacement only if bio->bi_opf has all the
0064 selected flags set.
0065
0066 Examples:
0067
0068 Replaces the 32nd byte of READ bios with the value 1::
0069
0070 corrupt_bio_byte 32 r 1 0
0071
0072 Replaces the 224th byte of REQ_META (=32) bios with the value 0::
0073
0074 corrupt_bio_byte 224 w 0 32
